First off - the Peter Principal

http://www.guardian.co.uk/education/2010/nov/01/random-promotion-research

If you've ever thought you boss was incompetent - it could be because he was too awesome at his last job and they foolishly promoted him 🙂

I think the completely different workload from being the 'go-to' thinker/doer to meetings, delegations and touchy-feely reviews is something that most people would struggle with and would find a long learning curve for that would present as 'incompetence'.

Personally, being a people-manager is not something I'd like to do, I can admire good people-managers particularly those who have good technical knowledge but for myself the challenge of making a team the most effective possible is much less interesting than implementing a new report system.